<!DOCTYPE html>
<html>
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		ul {
			background-color: red;
			overflow: hidden;
		}

		ul > li {
			float: left;
		}

		.clear {
			clear: both;
		}
	</style>
</head>
<body>

	<button>my btn1</button>

	<ul>
		<li>item1</li>
		<li>item2</li>
		<li>item3</li>
		<li>item4</li>
		<li>item5</li>
		<!-- <div class="clear"></div> -->
		<!-- <div style="clear:both;"></div> -->
	</ul>

	<button>my btn</button>
	
</body>
</html>